1. Field of the Invention
The present invention relates to an image pickup unit capable of changing an optical characteristic of an observation optical system and an endoscope provided with the image pickup unit.
2. Description of the Related Art
As is well known, an endoscope is widely used, for example, to observe or treat inside of a living body (inside of a body cavity) or to inspect or repair industrial plant equipment.
In recent years, in some endoscopes of this type, an image pickup unit capable of moving an observation optical system in a photographing optical axis direction to change a focal length has been used for a zooming function of adjusting focus of a photographing image or adjusting magnification of wide/tele and the like. Note that the technique of the image pickup unit capable of changing the focal length is used not only in the endoscopes, but also in various photography devices.
For example, an image pickup unit is known as disclosed in Japanese Patent Application Laid-Open Publication No. 2004-16337, the image pickup unit including an actuator for a focus switching system, the image pickup unit being configured to drive a moving lens unit (moving lens frame) provided in an observation optical system.
In such a focus switching type image pickup unit, relative positions of each fixed lens frame and the like generally need to be slightly adjusted during assembly of the image pickup unit in relation to an advance position of the moving lens frame in order to realize an appropriate focus state even if there are machining tolerances in each lens frame, each objective lens, and the like.
Therefore, a technique of an image pickup apparatus is disclosed for example in Japanese Patent Application Laid-Open Publication No. 2009-300761, the image pickup apparatus capable of simply making a slight adjustment to a predetermined set angle of view even if there are machining tolerances in components and variations of clearance in moving lens frames fitted to lens frames.
By the way, assembly accuracy of an objective optical system needs to be drastically improved in a recent image pickup apparatus along with shrinking of an image pitch of an image pickup device.